DESCRIPTION (Directly taken from the application) Polycystic kidney disease (PKD) is a group of disorders characterized by the development of fluid-filled cysts from the nephrons and collecting ducts of affected kidneys. The frequency of autosomal dominant (AD) PKD in the U.S. is one per 200-1,000 individuals, with progression to renal failure occurring in approximately 50% of those with the gene. Genes for ADPKD are now thought to be located at three chromosomal sites. Recently, the gene causing the most common form of PKD in humans, PKD1, was isolated and sequenced, as reported by three groups of European and American collaborators. While there are still some ambiguities in the sequences reported by these groups, there is an emerging consensus that the PKD1 gene product is a very large, membrane-associated (or matrix- associated) protein that may function as a receptor in cell-cell or cell-matrix interactions. A number of protein motifs have been found in the PKD1 protein by computer sequence analysis, suggesting that it is involved in a number of different kinds of protein-protein interactions. However, because the PKD1 protein is novel and because much of the protein does not show similarities to other known proteins, it is difficult to ascribe a specific biological function to it. The proposed studies will examine the mouse homolog of the human PKD1 gene. It is thought that, in contrast to the human gene, the mouse gene is not repeated, and will therefore provide an unambiguous cDNA sequence. The mouse is also more amenable to developmental studies to examine the expression of the PKD1 protein and its binding partners. The major thrust of this proposal is to identify extracellular and intracellular proteins with which the PKD1 protein interacts. Identification of these binding proteins will place the PKD1 protein in a known biological context or will identify new proteins that are a part of the biochemical pathway in which it functions. The specific aims are to 1) obtain the complete sequence of the mouse PKD1 cDNA, 2) construct fusion proteins specific to the N-terminal, putative extracellular domain of the PKD1 protein to identify tissues and organs to which the PKD1 protein binds, 3) screen expression libraries for cDNAs encoding N-terminal and C-terminal PKD1- protein binding proteins, and 4) characterize the cDNAs for these binding proteins, and examine the binding characteristics between the PKD1 protein and its binding proteins.